The present invention relates generally to transducers and in particular the present invention relates to in situ testing of transducers.
Pressure transducers are widely used in industry to provide active measurements of pressure. These transducers are typically calibrated during manufacturing and may need to be re-calibrated during its lifetime. Determining that a transducer requires re-calibration can be difficult. That is, an unexpected measurement output of a pressure transducer could indicate a problem with the transducer or an accurate measurement of an unexpected pressure condition. Additional testing may be necessary to determine if an accurate measurement was provided, or if the transducer is not operating properly. This additional testing may require that the transducer be removed from its operating environment for testing. This can create a problem in systems where the transducers cannot be easily accessed. For example, it is not possible to access transducers that are located in a deployed satellite or planetary exploration vehicle.
Presently, when a transducer failure occurs in a remote location, a great deal of effort and expense is expended to determine whether there truly is a problem with the transducer or whether a suspicious measurement is involved with the particular failed parameter. When space missions are planned, wide margins of safety are used to compensate for the degradation of the measurement devices installed over time. These safety margins result in extra fuel usage during launch, increased signal conditioning and telemetry requirements to support the extra measurements, and increased costs associated with these needs. During a mission emergency, the need to determine if there is a parameter or measurement failure increases the possibility of erroneous decision making, thereby unnecessarily jeopardizing the mission.
For the reasons stated above, and for other reasons stated below which will become apparent to those skilled in the art upon reading and understanding the present specification, there is a need in the art to accurately determine the health of a measurement device since its last calibration by an in situ check of the sensor""s major operating parameters. It would be even better if this could be periodically performed and adjustments made to compensate for the degradation of the device over time. This would yield a better evaluation of system performance for a longer period of time.
The above-mentioned problems with transducer testing and other problems are addressed by the present invention and will be understood by reading and studying the following specification.
In one embodiment, a pressure transducer test apparatus comprises a fitting to receive a pressure input, an output to receive a pressure transducer, and a valve attached to the fitting near the input. The fitting has a variable pressure chamber with first and second selectable internal volumes between the valve and the output.
In another embodiment, a pressure transducer test apparatus comprises a fitting to receive a pressure input, an output to receive a pressure transducer, a valve attached to the fitting near the input, and a piston provided in the fitting. The piston can be remotely moved between two positions. In the piston""s first position, the fitting has an initial volume between the valve and the output, and in the piston""s second position, the fitting has a different internal volume between the valve and the output
A method of in situ testing a pressure transducer comprises measuring a first internal pressure in a fitting using the pressure transducer, changing an internal volume of the fitting to change the internal pressure, measuring a second internal pressure in the fitting using the pressure transducer, and comparing the measured first and second internal pressures to historical pressure readings.
A method of health checking a calibrated transducer comprises recording a sensitivity, linearity, hysteresis and repeatability of the transducer during calibration, checking the sensitivity, linearity, hysteresis and repeatability of the transducer in the operation environment, and comparing the recorded values of the transducer with the checked values of the transducer to determine the health of the transducer.
In another embodiment, a pressure transducer test apparatus comprises a fitting to receive a pressure input, an output to receive a pressure transducer, a valve attached to the fitting near the input, and a piston provided in the fitting. The piston can be remotely moved between first and second positions. The fitting has a first internal volume between the valve and the output when the piston is in the first position, and the fitting has a second internal volume between the valve and the output when the piston is in the second position. The fitting also contains a temperature measuring device so that pressure and temperature may be measured simultaneously, and with sufficient rapidity, to allow the quantity of entrapped gas to be estimated thereby providing an estimate of the absolute pressure value. This allows the detection and correction of offset errors.